Tag Archives: Exserohilum

Aspergillus and Exserohilum: what turned them deadly?

The recent outbreak of Meningitis (July – October 2012) has been deadly. Of the approximately 13000 individuals exposed to tainted steroid back pain injection (click here for details) 18 had died until October 8, 2012. Fortunately, the average healthy individual is able to fight off the causal agents of this outbreak – two fungi. Well, lets get to know these fungi better.  The two fungi are Aspergillus and Exserohilum.  Here, we cover Exserohilum.

First described by Leonard and Suggs and subsequently reviewed by Sivanesan (see 11)

Exserohilum rostratum conidiophores
Fungal colonies are grey to blackish – brown
Source: Mycology, Adelaide University

Exserohilum sp. conidia
Note the strongly defined protruding truncate “exserted” hilum
Hilum is defined as the scar on the conidia at the point of attachment to conidiophore
Source: Mycology, Adelaide University

More commonly known as an invader of grasses (see 1;2), Exserohilum has rarely caused a disease in humans. While meningitis is known to have a fungal causal agent (see 5), it has never been by the genus Exserohilum (see 7,8). It is an emerging human pathogen and needs to be better understood (8). This genus while found to cause leaf spots and leaf stripes on certain plants (see 10), does not even invade healthy grasses, let alone healthy humans. Sivanesan described 20 species of Exserohilum in 1987 and is the established published source (see 11) on the illustrated biology, pathogenicity, toxin production and distribution of Exserohilum. Robert Leahy has added information on Exserohilum sp. leaf spots of Bromeliads (see 2). Bromeliads in their natural setting are fungus free. Since Bromeliads became increasingly desirable they are now cultivated under conditions where they are susceptible to destructive leaf streaks by this fungus. Hence, the study on how to recognize the symptoms and control them.

What turned the fungus deadly?

Very few scientists study human diseases caused by Exserohilum simply because they are so rare. They do cause  sinusitis (see 9). It has never been located in meningitis disease samples to date (see 8). Meningitis causing fungi are more commonly Aspergillus, Cryptoccocus and Candida (see 5), and Prof Robert Cramer’s laboratory is among the few who are studying the destructive process of human invasion by Aspergillus(see 5).

Certain types of Exserohilum are known to produce toxins, which could perhaps weaken or destroy/kill a weakened host like a plant or a human. A list of some of the toxins it produces are: Glyceolin, Cynodontin, Exserohilone, Monocerin, Monocerin, Ophiobolin A, and Ravenelin (see 10). The first two are produced by E. rostratum, the most commonly studied.

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